Why are senior level posts vacant ?

The hot topic in the power galleries these days is related to the vacant posts in the govt of India. Sources said that this govt is not like UPA govt, where appointments were cleared only on recommendations. But the present government goes into deep investigations. When it is satisfied, then only appointments are made against the vacant posts. Many officers were reportedly found ineligible and rejected. And that is the reason that some officers are holding two to three responsibilities.